1. Field of the Invention
The present invention is directed generally to an improved optical communications system that utilizes an acousto-optic modulator device as a signal transmitting transducer for electrical signals carrying information and, more particularly, to an optical beam that has been modulated by an acousto-optic modulator that can be detected by a photodetector and appropriate electrical transducer circuits to demodulate the optical beam and recover the original electrical information.
2. Description of the Related Art
U.S. Pat. No. 5,146,358 describes an architecture of optical and electrical components that constitute an optical communication system.
U.S. Pat. No. 5,146,358 further describes that diffracted optical beams in conjunction with a remaining or undiffracted optical beam may be spatially recombined by an optical lens to create a single composite optical beam that can propagate through free space or an optical waveguide, directly to a photodetector that performs the optical demodulation function to recover the original electrical signal.
U.S. Pat. No. 5,146,358 further describes the manner in which a diffracted portion of the optical beam experiences modulation of optical amplitude and frequency by means of the acousto-optic interaction effect, and specifically that the optical amplitude and frequency modulation is equal to the amplitude and frequency of the input electrical signal. Further, the undiffracted portion of the optical beam does not experience any acousto-optic modulation, and thus serves as a reference signal beam carrying the original amplitude and frequency parameters of the input laser beam. A remote photodetector in the reverse biased photo current mode serves as a classical signal mixer so that the incoming diffracted beams and the incoming undiffracted beam provide the signals required to perform homodyne mode detection and recovery of the original electrical signal. This architecture is useful for carrying electrical information in that the architecture provides a self-referencing signal modulation system, i.e., the desired electrical signal parameters are represented by the amplitude and frequency differences between the undiffracted reference beam and the diffracted signal beams present in the composite beam. This architecture of optical differences provides a means for signal transmission and recovery that is independent of absolute laser amplitude and frequency variations or instabilities. Further, the architecture provides a means of providing a coherent signal channel that provides a means of transmitting complex electrical signals over some useful distance to a remote photodetector receiver that can recover the complex electrical signal.